Another thumbs up from me on the Gens Ace Lipos. I run the 50c 5000mAh packs, and some older 25/40C hardcase packs in my B4.1. They are BRCA approved and super cheap. Excellent performance, and well worth it.
I've just noticed that giantcod/shark now stock the gens ace saddle packs. I'd be tempted to say go for saddle packs, even at 25C/50C peak. These will be more versatile in losi 22/centro and other buggies that take sticks.
I'll be buying one to test, before I make the move to a centro chassis, which needs saddles. 25C (50C peak) packs are fine for 2wd. People have found higher C rating cells a bit overkill and harsh for 2wd, especially in low grip/traction situations.
Some objective reviews of the gens ace packs:
https://www.youtube.com/watch?v=n1d07VuMgzI
https://www.youtube.com/watch?v=wwBVWFLbwS8
Boost. Yes it's essentially increasing the timing on the fly either after the throttle has been full for a short delay or all the time when a rev range is hit. I run a Tekin RS Pro, which has excellent boost and timing controls, but not for everyone as it requires a laptop/USB interface and software to make the tuning. You can essentially tune a higher wind motor to perform a lot faster.
I also came back to RC recently after 20 years off, but have picked it again quick enough. I considered all the 2wd options like you are now, but settled on the B4.1 first, and will upgrade to a C4.1 centro very soon (would have been quicker if i'd bought saddles initially ;-).
Lots of people at my local club (Batley) run durangos and AE B4 based mid motors, either vega, X6 or centro.